The invention is based on a seat test body for vibration tests for seats, for example of a motor vehicle.
A seat test body is known, for example, from German Patent Document DE 41 03 374 C1. The inventors also described that seat test body in Automobiltechnische Zeitung ATZ 97 (1995), Volume 10, Pages 668 to 671.
One of the aspects of developing seats, particularly vehicle seats, is that a high sitting comfort is desirable. The reason is that occupants of vehicles, and particularly the driver, may have to remain in the vehicle seat for many hours while they can move very little. Among other aspects, a good vibration capacity of the seat also plays a role in this case. In the course of the development of a seat, various seat and cushion constructions are produced as test samples, which must be compared with one another objectively and reproducibly with respect to different testing and evaluating criteria, mainly concerning the comfort and the vibration capacity, in order to be able to then select the best test samples. Not only new test samples of a current seat development but also various test seats of different origins, for example, seats of earlier generations of seats; used seats or seats from outside development or manufacturing facilities of any pairing are compared with one another.
For vibration testing, the seat together with a test person sitting on it or with a seat test body placed on it, is excited to perform vertical vibrations, and the response vibrations of the test body or the test person are measured. During the vibration measurements, flat cushion-shaped acceleration sensors are placed on the contact zone of the buttocks with the surface of the seat cushion and this vibration is measured as a response vibration. The obtained response vibrations are entered in a diagram as the spectral distribution of the vibration amplitudes in relation to the corresponding excitation amplitude. These so-called transmission curves are--starting with a very slow, quasi-static excitation--determined into the range of approximately 30 Hertz. Typically, the transmission curves start at a value of 1.0 and will then have a clear resonance point in the range of approximately 5 Hz. Then, it will, as a rule, clearly fall under the value of 1 and will extend--in a range of the seat damping--in a slightly falling manner with an increasing excitation frequency.
The initially mentioned known seat test body consists of a seat shell which has a rigid surface and corresponds to the shape of the buttocks, including the thigh part of a human being, and of a rigid back shell which is connected with the seat shell and which corresponds to the shape of the back. Several damped spring/mass systems which can vibrate vertically are installed in the seat shell for simulating the vertical vibrating tendency of parts and regions of the body, the weight and the mass distribution of the spring/mass systems corresponding approximately to the one-seat weight of a person of average weight. The buttocks shell and the back shell of the seat test body are rigidly arranged with respect to one another at an angle which corresponds to the sitting position of a human being, in which case the back shell only has the function of supporting the seat test piece during the vibration test on the backrest cushion and to stabilize it in position on the seat. Before a vibration test of a seat with the known seat test piece, this seat test body, together with the seat shell, is placed loosely on the seat cushion of the seat and the back shell is leaned against the backrest cushion.
The applicant carried out comparative measurements using the known seat test bodies, on the one hand, and test persons, on the other hand, in various seats. The comparison of the measurements showed that the measurements provide correct information only in the area of the resonance rise and even there only tendentiously correct information. The resonance rise determined by the applicant by means of the known seat test piece quantity quantitatively did not correspond to the values measured by means of test persons. According to the applicant's experiences, the measuring results of the known seat test body in the area of the seat damping are even less comparable. Above approximately 7 Hz, the transmission curve determined with the seat test body extends in an ascending manner and toward the end of the measuring range even reaches rise values which partly are clearly over the resonance rise, whereas the test person measurements showed a drop of the transmission values to below 0.5. A comparison of a well-damping seat with a less well-damping seat shows that the known seat test body in the area of the seat damping furnishes not even tendentiously useful measuring values. This comparison demonstrates that--at least according to the applicant's experiences--the know seat test body can furnish information which can be compared with information concerning test person vibration measurements only to a very limited degree and cannot replace this type of measurement. Therefore, vibrations tests of seats could be carried out only by using test persons. These naturally require high expenditures with respect to time and personnel and, in addition are hardly reasonable.
It would be conceivable to carry out such vibration tests by means of test dummies. Test dummies of the third generation are described, for example, in "SAE 1994 Transactions"--Journal of Passenger Cars, Section 6, Volume 103, Pages 1868-1886. With respect to the mechanical moving behavior and the mass distribution of the overall body, they have an anthropomorphous design. However, with respect to individual body regions or members, the dummies partly have a fairly rudimentary construction and with respect to details cannot be considered to be an anthropomorphous construction. This applies particularly to the seat part of the pelvic area which is of interest here. This area is completely unimportant for full dummies, as used for accident tests, although it is stated there in connection with the pelvis that it consists of an aluminum casting structure whose shape is approximately similar to a human pelvic bone structure. It is stated that this pelvis is enclosed by a soft rubber material in order to approximate the shape of human buttocks which also contains a three-axis acceleration generator.
Beyond the mentioned information from the indicated literature, the following can be stated on the basis of experiences with and observation of Hybrid III Dummies used everywhere in the pertinent development and testing facilities--thus, also by the applicant--in several models and in different heights. The hard parts, as, for example, soft parts surrounding the pelvic body are constructed as double-walled hollow pieces made of a soft rubber whose wall thickness amounts to approximately 3 to 5 mm. The hollow space enclosed by the double walls is filled with flexible foam. Such a double-wall hollow soft part is assigned to each individual limb--lower leg--thigh--pelvis--upper body--upper arm--lower arm--hand. The double-walled hollow parts are longitudinally slotted so that they can be pushed in each case over the pertaining hard part and can be closed with a zipper. The inside contour of the hollow soft part is roughly adapted to the hard parts of the limb to be enclosed, that is, with a certain play, whereas the outside contour corresponds approximately to the outside shape of the corresponding part of the body. The soft parts of the individual dummies do not adjoin one another directly; a large gap is left open between adjacent soft parts so that the limbs of the dummy can move without being hindered. Thus, a gap of 3 to 4 cm extends in the transition area from the thigh into the buttocks part or at the transition from the buttocks into the back. With a view to the high loads applies to the testing dummies in the case of simulated accidents and with a view to their repeated usability--they are very expensive--the soft parts must have a certain minimum stability at least on their exterior side and must not be too soft because these soft parts would otherwise be destroyed during accident simulations. The soft parts enclosing the pelvic area have a Shore hardness of approximately 40 to 50 degrees of hardness in the buttocks area which is distributed largely uniformly along the seat part of the buttocks. The outer shape of the dummy's buttocks--deviating from the human model--has a relatively flat shape. It should therefore be pointed out that, in the buttocks area, there exists only a rough approximation to the human anatomy which, however, is completely sufficient for the use as a test dummy in crash tests even in the third generation of dummies. By means of the only approximated flat reproduction of this seat contour, the tilting and sliding action of a dummy sitting in a cushion, which is relevant in the case of a crash, is to be approximated to the sitting stability of a real human being. A surface shape which is approximated to the shape of the buttocks and an elasticity in the buttocks area of the test dummy which approximately matches close to the surface is sufficient for this purpose. However, according to experiences obtained by means of the invention, comfort and vibration tests on seat cushions of vehicle seats cannot be accurately determined with such a test dummy.
It is an object of the invention to provide a seat test body whose measuring results determined during vibration measurements on vehicle seats in the whole spectral range are comparable at least qualitatively with corresponding test person measurements.
This and other objects have been achieved according to the present invention by providing a seat test body for vibration measurements on seats, comprising: a buttocks imitation to be placed on a seat cushion of a seat to be tested and which points downward in a testing position, a back imitation coupled with the buttocks imitation and which is to be leaned against a backrest cushion of the seat to be tested in the testing position, and passive ballast in the form of several weights placed on at least one of an interior side of the buttocks imitation and an interior side of the back imitation, said seat test body having a weight and mass distribution corresponding approximately to the weight and mass distribution of a sitting person, the buttocks imitation and the back imitation each being formed hard parts and padding, the hard parts of the buttocks imitation simulating a pelvic bone, thighs, and hip joints of a human skeleton at least with respect to the underside of the skeleton which would be loaded while sitting, the hip joints being fixable to immobility under a test load, the hard parts of the back imitation simulating the lordotic area of a pelvic bone, a spinal column, and a back side of a chest cage including a shoulder blade region, of the human skeleton, the padding of the hard parts of the buttocks imitation anthropomorphically imitating the soft parts of a human buttocks area, including muscle tissue, connective tissue and fatty tissue, and the two sitting pressure points of the human buttocks, with respect to the parameters of shape, position, hardness, hardness distribution, layer thickness, softness, elasticity, damping behavior, imitating the hard parts and the soft parts of the human skeleton as close to life as possible.
A definitive idea of the invention is to provide a simulation of the vibration-related coupling of the seat test body, which is as true to life as possible, to the seat cushion and the backrest cushion. The transition from the cushions into the seat test body with respect to vibrations is to be simulated as exactly as possible to the corresponding "interface" between man and machine. The dominating phenomenon in this case is an anthropomorphous construction and distribution of the soft parts in the single seat area starting from the underside of the thighs and extending into the shoulder area. It is important in this case that the seat test body causes not only a deformation of the cushion surface corresponding to a sitting person but also a sitting pressure distribution which corresponds to the natural sitting position. This is accomplished via the construction of the seat test body which is soft according to the invention. According to the applicant's experiences, inherently dynamic influences of individual parts or regions of the body fade into the background in comparison to an anthropomorphically "soft" coupling of the seat test body to th e seat.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.